1. Field of the Invention
This invention relates to an ADSL (Asymmetric Digital Subscriber Line) modem apparatus that performs communications using multiple carriers, and a re-initializing method for the ADSL modem.
2. Description of Related Art
In order to perform a communication using an ADSL communication control apparatus (hereafter referred to as ADSL modem), the communication must adheres to the G.992.1 (G.DMT) standard set by ITU-T. In this standard, the DMT (Discrete Multi Tone) method is employed as a modulation/demodulation method for ADSL modems. DMT method is a multi-carrier modulation/demodulation technique that uses multiple carriers with different frequencies.
Upon starting a data communication, an ADSL modem performs an initialization with an ADSL modem in a reception side, in order to determine sub-carrier to be used for the data communication among sub-carriers configuring multi-carrier. Further, the ADSL modem determines data amount to be allocated into each sub-carrier. The data communication is performed according to this initialization setting. Accordingly, the data communication is achieved in accordance with communication status at the time the data communication has begun.
When it becomes difficult to maintain the current communication with the communication status because of a line abnormality or the like during data communication, the ADSL modem that has detected the communication difficulty requests the other ADSL modem for a re-initialization. Then, the data communication resumes according to the re-set setting based on the re-initialization.
However, the above-described ADSL modem performs a re-initialization only after an adverse communication status is detected, a condition that makes it difficult to maintain the current communication, and resumes the data communication after the re-initialization. Therefore, a data communication will be performed according to the initialization setting when the communication begins, and continues until an adverse communication status is detected, a condition that makes it difficult to maintain the current communication. For example, even when the communication status improves after the data communication has started, the data communication is still being performed according to the initialization setting at the time the communication began. Thus, the data communication is not performed according to the most recent change in communication status that has occurred after the data communication began.